Catheters are commonly used to perform a wide variety of medical procedures within human body lumens. Often, depending on the type of procedure involved, a catheter may desirably be used to perform multiple functions. It is common for such catheters to have multiple lumens, each dedicated to the performance of a particular function. For example, in many types of balloon catheters, it is common for the catheter to have two lumens, one for inflation or deflation of the balloon, and another to provide direct communication from the proximal to the distal end of the catheter, such as to deliver medication, contrast liquid or the like or to withdraw blood or other fluid from the body lumen. By way of further example, one such balloon catheter commonly in use is that employed in percutaneous transluminal angioplasty (PTA) procedures, in which a balloon dilatation catheter is inserted into a patient's artery for the purpose of enlarging a blood vessel which has become obstructed as a result of arteriosclerosis. Such angioplasty catheters typically are guided through the patient's arterial system to the site of the obstruction (the stenosis) by a guidewire over which the catheter is passed. After the guidewire has been passed through the stenosis, the catheter then is advanced over the guidewire to place the balloon (while in a deflated condition) within the stenosis. Once so placed, the balloon is inflated with an inflation liquid under a high-pressure, sometimes as much as the order of about 20 atmospheres, to forcibly dilate the stenosis and enlarge the lumen in the artery, thereby improving blood flow through the artery. such catheters require two lumens, one for inflation or deflation of the balloon and the other for reception of the guidewire. Typically, the guidewire lumen also may be used to deliver liquids out of the distal end of the catheter or to take blood pressure measurements.
It is a desirable objective of such catheters to maximize the cross-sectional flow area of each of the lumens. For example, it is advantageous to provide a relatively large cross-sectional flow area for the inflation/deflation lumen in order that the time required to inflate and deflate the balloon is kept at a minimum. It also is desirable to maintain a relatively large cross-sectional area for the guidewire lumen to facilitate freedom of movement of the guidewire within the lumen as well as to provide a relatively large fluid flow area for infusion of liquids and for measurement of blood pressure. A significant competing consideration, however, is the importance of maintaining the outer diameter of the catheter as small as possible. Maintaining a small outer diameter for the catheter is important in order to permit the catheter to be advanced into relatively small diameter arteries as well as to facilitate advancement of the deflated balloon of the catheter into the stenosis to be treated. If the diameter of the catheter is too large, it may not be able to reach into a small artery or, even if it can be inserted into the artery, it may not be able to cross the stenosis. As a result, the catheters of the prior art typically have reduced the size of one lumen in order to increase the size of another.
There is a need, therefore, for a catheter configuration in which the cross-sectional area of each of the lumens may be maximized without increasing the outer diameter of the catheter. It is among the general objects of the invention to provide a catheter construction that satisfies that need.